Mandrel for making small radius tubular bends



Sept. 1, 1959 FUCHS, JR" ETAL 2,902,078

MANDREL FOR MAKING SMALL RADIUS TUBULAR BENDS Filed June 23. 1954 INVENTORJ FRANCISJ.FUCHS,J r. ROBERT H. HALL fin-Vi ttes MANDREL FOR MAKING SMALL RADIUS TUBULAR BENDS Application June 23, 1954, Serial No. 438,759

-1 Claim. 01. 153-63) This invention pertains to apparatus for use in bending tubes, and more particularly to a mandrel for use in effecting small radius seamless bends in rectangular wave guide tubes.

High frequency electromagnetic energy is commonly transmitted by means of thin-walled rectangular tubes or wave guides. Such wave guides will transmit two general types of electromagnetic waves, the so-called E waves and H waves, the former having an electric field component in a plane parallel to a narrow side of the transmitting wave guide, and the latter having a magnetic field component in a plane parallel to the broad side of the wave guide. Consequently a wave guide which is bent in the plane of the narrow side thereof is termed an E bend, and guide which is bent in a plane parallel to the broad side thereof is termed an H bend. It is necessary in effecting such as bends in wave guides to uniformly support the interior thereof with a flexible mandrel in order to preserve as far as possible the original interior cross-sectional dimensions of the tubes, and it is also desirable to prevent or to reduce to a minimum any scratching of the interior surface of the wave guide by the supporting mandrel in order to eliminate arcing of the high frequency energy or other unwanted changes in the electrical transmission characteristics of the wave guide.

Therefore, it is an object of the present invention to provide an articulated mandrel for supporting the interior of a rectangular wave guide tube during the bending thereof.

It is another object of the present invention to provide a mandrel for supporting the interior of a wave guide tube while the tube is bent into the form of an E bend of relatively small radius, for example approximately inch.

It is a further object of the present invention to provide a mandrel which will eliminate or substantially reduce scratching of the interior surface of a wave guide tube during the bending thereof.

It is a still further object to provide a tube bending mandrel having great mechanical strength and capable of maintaining substantially unchanged the interior crosssectional dimensions of a wave guide being bent.

In accordance with the above objects, a preferred embodiment of the present invention comprises a rigid stem and a flexible body secured at one extremity thereof to the stem and including a series of body links, each of these links comprising a body portion and an apertured arcuate lug centrally projecting from one extremity of the body portion and forming an arcuate indentation therewith. A shouldered recess is formed in the body portion of each link opposite the lug thereof. There is also provided an end link or member similar in configuration to the body links, but having no shouldered recess therein. Means are provided to pivotally retain each of the lugs in the recess of an adjacent link whereby the links are permitted a predetermined unilateral deviation from a linearly aligned position, this deviation being Patented Sept. 1, 1959 limited by the engagement of the shoulders of the recesses with the indentations of adjacent links.

Other objects and advantages of the present invention will become apparent from an examination of the following detailed description when taken in conjunction with the accompanying drawings, wherein:

Fig. l is a top plan view of the unactuated mandrel;

Fig. 2 is a side elevational view of the unactuated mandrel;

Fig. 3 is a cross-sectional View of the mandrel taken on line 33 of Fig. 1;

Fig. 4 is a cross-sectional view of the mandrel taken on line 44 of Fig. 2;

Fig. 5 is a cross-sectional plan view similar to Fig. 4, but viewed in the direction opposite to that indicated by line 44 of Fig. 2 and showing the mandrel in an actuated position within a bent tube;

Fig. 6 is a perspective view of a portion of the rigid stem of the mandrel;

Fig. 7 is a perspective view of a representative body link, and

Fig. 8 is a perspective view of the end member.

Referring now to the drawings wherein similar reference numerals designate corresponding parts throughout the several views, the numeral 11 designates generally a rigid stern slidably insertable within a tube to be bent and having a first extremity thereof adapted for connection to a reciprocable mandrel shaft (not shown). A second extremity of the stem 11 is provided with a pair of spaced-apart convex projections 12 (Fig. 6). A cavity 13 extends transversely of the stem 11 between the projections 12 and is defined by the projections 12, by an arcuate wall 14 and by an upper plane wall 16 tangent thereto. The stem 11 is also provided with an upper shoulder 17 having a curved outer surface extending transversely of the second extremity of the stem and having a.

planar inclined surface 18 intersecting the plane wall 16 of the cavity 13 and the convex surfaces of the projections 12. A lower shoulder 19 extends transversely of the stem 11 between the projections 12 and intersects the arcuate wall 14 of the cavity 13. The stem 11 is further provided with a pair of aligned apertures 21 extending transversely thereof through the projections 12 and interconnecting with the cavity '13.

A flexible or articulated body denoted generally by the numeral 22 (Fig. 2), includes a series of body links 23, each of which has a body portion similar to the one denoted generally by the numeral 24 (Fig. 7), and is provided with a discontinuous cylindrical surface 26, a plane surface 27 tangent to the cylindrical surface 26, a beveled surface 23 extending transversely of each link 23 and intersecting the plane surface 27, and a pair of spaced-apart concave surfaces 29 extending between the cylindrical surface 26 and the beveled surface 28.

A lug denoted generally by the numeral 31 extends from the body portion 24 between the concave surfaces 29 and is provided with an aperture 32, a Hat surface 33 intersecting the beveled surface 28, and a convex surface 34 intersecting the cylindrical surface 26 and defining therewith an arcuate indentation 36 (Fig. 4).

The body portion 24 of each link 23 is also provided with a recess 37 extending transversely thereof opposite and extending into the lug 31 (Fig. 3) and opening on the cylindrical surface 26 to define thereon a pair of spaced-apart convexities 38. The recess 37 of each link 23 is partially defined by a curved wall 39 and by a straight wall 41 (Fig. 4) tangent thereto. Inasmuch as the recesses 3737 extend through the body portions 2424 and into the lugs 3131, links 23-23 may be connected pivotally in closely adjoining relationship so as to effect small radius bends of the articulated body 22. A shoulder 42 extends transversely of the body portion does not have a recess- 37 nor-' apertures 43' Thus the end member 44'isprovided-withalug 5 sirnil'ar' tothe lugs-3l of the links Z'Zfand havingan aperture :76 extend ing theretlirough.

A pivot pin 46 (Fig. 3) extends through the aligned apertures-21 of the stem 11 and-through aperture'32' of a first terminal body link 23 topivot ally retain a' 1i1g-31 thereofwit hinthe cavity 13 0f the stern in such a manner that a flat surface 33 (Fig. 4) ofthe l-u'g"31' is adjacent the plane wall 16' of the stem, a

beveled surface 23" of'tli'e' first terminal link 23" islocatedadjacent the inclined surface 18 of the upper shoulder 17 of the stem 11; and the convex projections 1210f the stenrll are slidably engageable with concave surfaces 29 on the first terminal link whereby the latteris permitted a predetermined" lateral deviation in one direction from a position of linear alignment with the stem 11; this-deviation being limited by the engagement of the lower shoulder 19 of the stem 11 with an arcuate indentation 36' of the first terminal link.

Lateral movement between the first terminal link 23 and the stem 11 in the opposite direction is prevented by the engagement of the inclined surface 18 adjacent shoulder 17 of the stem 11 with the beveled surface 28 of the link 23, and by the abutment of the plane-"wall 16 'ofthe stem 11 with the flat surface 33 of the'lin'k' Means such as pivot pins 47 and 48 (Fig. 3) are-provided to pivot-ally retain the lugs 31 of successive body links within the corresponding cavities 37 of adjacent preceding body links whereby all of the links 23 comprising the flexible body 22 are permitted relative rnove-* ment similar to the movement between the stem 11and the first terminal link 23.

Additi'onalmeans such as a pivot pin 49 is provided to similarly interconnect the end member 44 and a second terminal link 23".

In a draw bending process, such as is described and shown in-a co-pending application of Francis J. Fuchs; Jr., Serial No. 262,246, filed December 18, 1951, now Patent No. 2,778,402, a rearward extremity of a tube to be bout is restrained against lateral movement and a forward extremity thereof is securely clamped between a -rotatable forming die and a clamping die mounted upon-a common bending head with the forming die and movable therewith:

A flex-ibl'e'rnandrel, such as the one disclosed herein, is" secured to-a reciprocable mandrel shaft and fed for wardly-into the tube to a position opposite the bending Upon actuation of the bending head the tube is" dies. drawnforwardly over the stationary mandrel and as sumes the shape of an adjacent die surface 'of the form ing die. When a tube is bent with such apparatus, the greatest bending force-is applied 'tothe tube at a position coincident with-the initial point of bend, that-is; at a" tioned from the stem 11 has the lug 3'1'and the recess 37 thereof of smaller transverse dimensions than those of the corresponding'structures of the precedinglinks nearer the stem (Fig. 3). The lug 31 of each link 23 is complementary in size to the recess 37 of an adjacent link, and when positioned therein is capable of a limited rotary sliding movement relative thereto. The cavity 13 of the stem 11 is complementary to the lug 31' of the first terminal-link 23 located adjacentthereto, and similarly, the lug 45 of the end member 44 is complementary to the recess 37" of the second terminal link 2 In operation the stem 11 of the assembled-mandrel is connected at the first extremity thereof to a reciprocable mandrel shaft, and the mandrel'is fed forwardly into the interior of a tube to be bent ina manner and with an apparatus similar to that disclosed in the aforementioned co-pendin'g application? Thebending apparatus is actuated to bend the tube into a curved form as designated by the numeral 51, whereupon the links comprising the'flexible body 22 rotate about the connecting pivot pins and assume the configuration of the bent'itube', thereby affording uniform support to the interior thereof (Fig. 5).

At the completion of the bending operation the mandrel is retracted from the bent tube 51 and the tube is' then removed from the bending apparatus.

The minimum radius R (Fig. 5) throughwhich a tube can be bent with the mandrel disclosed'h'erein is dependent'upon the positions at which the lower shoulder 1901? the stem hand the shoulders 42 of the body links 23'engage the surfaces defining the arcuate indentations 36 of adjacent links.

The mandrel as disclosed herein'is particularly well suited tothe accurate bending of Wave guide tubes of small dimensions because of the substantially uniform support afforded the tubes by the closely spaced links'23. Furthermore, the incidence of mandrel-produced scratches or seams on the interior surfaces of the wave guides is materially reduced due to the fact that the rotary sliding? A tube bending mandrel comprising a rigid stem and a' flexible body attached at one extremity thereof to said stem, said flexible body including a series of pivotallyinterconnected links, each of said links being provided with a lug projecting from one side thereof and a recess opening opposite and extending into said lug for reception therein of an adjoining lug, said lug and said'recess'of each link successively further removed from said stem having transverse dimensions thereof smaller than the" transverse dimensions of similar elements of links nearer said stem.

References Cited in the file of this patent UNITED STATES PATENTS 1,021,450 Cox Mar. 26, 1912 1,075,045 Lewis Oct. 7, 1913 1,683,573 Mueller Sept. 4, 1928' 2,545,878 Forrest Mar. 20, 1951 FOREIGN PATENTS I 5,019 Great Britain Apr. 23, 1885 347,405 Italy Apr. 8, 1937" 700,370 Great Britain Dec. 2, 1953 f] a... n? 

